Conventionally, photovoltaic charging devices are proposed, which charge a secondary battery with electric power generated by a solar cell so as to supply a current to a load (see Patent Documents 1 and 2). In such conventional technology, the electric power generated by the solar cell is controlled by a control circuit. For example, the electric power is subjected to pulse width modulation (PWM) control so as to have a waveform (voltage waveform and/or current waveform) suitable for charging the secondary battery.
When the conventional photovoltaic charging device is used for installed equipment such as a residence or a streetlight, a lead-acid battery is adopted as the secondary battery, and the lead-acid battery is continuously connected to a terminal of the control circuit. In this way, when using the photovoltaic charging device for the installed equipment, the charged state of the secondary battery can be appropriately and constantly controlled by the control circuit, which prevents the secondary battery from being in an overdischarged state.